This project will combine gene probe analysis with laboratory and field studies to assess the effect of an innovative aquifer remediation technology, co-solvent flushing (using 95% ethanol), on the indigenous microorganisms. In addition to studying indicators of ecosystems functioning, this project will also investigate the potential of the microbial populations present at a specific site originally contaminated with perchloroethylene (PCE) and trichloroethylene (TCE) to degrade residual contaminant and degradation products remaining after treatment. The specific hypotheses to be tested are: 1) microorganisms present at the site are capable of rebounding to their original diversity and activity recognized before flushing; and 2) these rebounded microorganisms are capable of degrading any contaminant and daughter products remaining after flushing, thus rendering the site harmless to human health and the environment. This proposed work has three specific aims: SPECIFIC AIM 1/GENE PROBE ANALYSIS: Specific prokaryotic gene concentrations will be measured before and after treatment and will be used as ecological and biodegradative indicators. These indicators will then be related to laboratory (Specific treatment and will be used as ecological and biodegradative indicators. These indicators will then be related to laboratory (Specific Aim 2) and in situ microcosm (Specific Aim 3) results in order to provide a means of assessing the natural degradative ability of the communities present. SPECIFIC AIM 2/LABORATORY MICROCOSM STUDIES: Microcosms will be set up to model the environment present before and after ethanol-flushing at a PCE- and TCE-contaminated site in Jacksonville, FL (in terms of oxygen levels, nutrient and contaminant concentrations). Rates of contaminant transformation and product formation (including TCE, cis- and trans-dichloroethylene (DCE), vinyl chloride (VC), ethene (ETH), chloral hydrate dichloroacetate, etc.) will be measured and compared before and after treatment. SPECIFIC AIM 3/IN SITU MICROCOSM STUDIES: In situ microcosms will be built and then placed at various locations at a PCE- contaminated site. In situ rates of substrate transformation, product formation, and electron donor/acceptor utilization will be measured and compared to the laboratory microcosm studies as another assessment tool for determining the activity of the microorganisms present before and after flushing at the site.